1. Field of the Invention
The present invention relates to an optical head which emits a light beam onto an optical disk, and detects the light beam reflected therefrom, and an optical disk drive provided with the optical head.
2. Description of the Related Art
An optical disk drive has an optical head provided with an objective lens and a photodetector, etc. The optical head radiates a light beam onto a recorded surface of an optical disk, and detects reflected light from the optical disk. Based on the detected reflected light, information recorded on the optical disk is read.
Also, the optical head radiates a light beam onto a recording surface of an optical disk to record desired information on the optical disk.
It will be explained how various signals are generated based on the reflected light from the optical disk.
The reflected light from the optical disk is guided to predetermined light detection areas of the photodetector by the objective lens and optical elements. The photodetector converts the guided reflected light into an electrical signal. Based on the electrical signal obtained by the photodetector, a tracking control signal is generated. Also, based on the electrical signal obtained by the photodetector, a focusing control signal is generated. The tracking control signal is applied to a tracking control for making the spot of light projected onto the recorded surface of the optical disk coincide with a track center on the recorded surface. The focusing control signal is applied to a focusing control for changing the position of the objective lens such that the spot of focused light is formed on the recorded surface. Based on the electrical signal obtained by the photodetector, a reproduction signal of information recorded on the optical disk is generated.
The objective lens is held by a lens holder. The lens holder is supported by one end portion of a number of elastic supporting springs. The small movement of the lens holder is controlled by a tracking coil and a focusing coil. Thereby, shifting of the lens is achieved, and focusing and tracking are also achieved.
Furthermore, in recent years, digital versatile disks (DVDs) have spread remarkably, and dual-standard equipment, i.e., optical disk drives that can handle both DVDs and compact disks (CDs) has come to the market. As is well known, the recording density of a DVD is greatly different from that of a CD. Accordingly, the wavelength of a light beam applied to a DVD is also different from that applied to a CD. Thus, the dual-standard equipment needs to process two beams having different wavelengths. Such dual-standard equipment is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2003-16672.
As a method for generating a focusing error signal, a knife-edge method is known. In the knife-edge method, a knife-edge is provided in a position midway in an optical path in which light reflected from the disk is converged, and the movement amount of a light spot image on a photoreceptor is detected, to thereby generate a focusing error signal.
Furthermore, when the knife-edge method is applied to focusing, optical diffraction elements such as holograms and optical detection elements for generating focusing and tracking error signals must be separately provided for DVD and CD, respectively. For example, in the technique disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2003-16672, an optical detection element and an optical diffraction element for DVD are provided separate from a laser for DVD, and an optical detection element and an optical diffraction element for CD and a laser for CD are provided as a single unit.